Blow molding apparatus

ABSTRACT

Blow molding apparatus and method for making a hollow plastic spool include a four section mold operated in a particular sequence to confine a thermoplastic core by two of the mold sections forming an open ended cavity while such core is permitted to expand outside the open ends of the cavity; coring pins carried by the other two mold sections deform the longitudinal axis of the protruding core and the other two mold sections close the cavity to finalize the shape of plastic spool and to pinch off excess plastic which has blown outside the peripheral edges of the mold cavity.

United States Patent 11 1 Saslawsky Dec. 4, 1973 BLOW MOLDING APPARATUS[75] Inventor: Sheldon Saslawsky, Easton, Conn.

[73] Assignee: Textron Inc., Providence, RI. 22 Filed: Sept. 27, 1971[21] Appl. No.: 184,144

[52] US. Cl. ..425/310, 425/342, 425/387 B,

425/DIG. 205, 425/DlG. 212 [51] Int. Cl B29d 23/03 [58] Field of Search425/326 B, 387 B,

425/324 B, DIG. 58, 451, 342, 243, 249, 296, 297, 310; 249/79 [56]References Cited UNITED STATES PATENTS 3,339,232 9/1967 Battenfeld etal. 425/342 3,048,891 8/1962 Maass 425/326 R23,564 10/1952 Hobson425/326 12/1959 Hagen et al 425/326 2/1967 Hill et a1. 425/326 PrimaryExaminer-J. Spencer Overholser Assistant ExaminerMichael 0. SuttonAttorneyAlexander R. Field [57] ABSTRACT Blow molding apparatus andmethod for making a hollow plastic spool include a four section moldoperated in a particular sequence to confine a thermoplastic core by twoof the mold sections forming an open ended cavity while such core ispermitted to expand outside the open ends of the cavity; coring pinscarried by the other two mold sections deform the longitudinal axis ofthe protruding core and the other two mold sections close the cavity tofinalize the shape of plastic spool and to pinch off excess plasticwhich has blown outside the peripheral edges of the mold cavity.

4 Claims, 8 Drawing Figures PATENTEI] DEC 41975 sum 3 or 3IIIIII'II'IIIIIIIIIII Jy a IIIII'II'I BLOW MOLDING APPARATUS BACKGROUNDOF THE INVENTION 1. Field of the Invention The present invention relatesto blow molding process and apparatus for making hollow plastic spoolsand, in particular, to such process and apparatus for sequentiallyshaping thermoplastic material into a hollow spool by a multi-sectionmold.

2. Description of the Prior Art:

U. S. Pat. No. 3,048,891 and US. Pat. No. 3,507,942 are representativeof conventional methods and machines for blow molding hollow articlesfrom a thermoplastic material. While the prior art is cognizant ofmulti-section mold apparatus and of sequentially forming a plasticspool, such prior art encloses the thermoplastic material within themold cavity whereby subsequent operations on the material takes placewithin the cavity with the resulting disadvantages that the finallyshaped spool may be weakened by uneven distribution of the material,that the spool flanges are not strong enough to withstand impact and/orcompressive loads, and that there is no provision for removal of excessmaterial from the mold apparatus or from the finally shaped spool.

SUMMARY OF THE INVENTION The present invention is summarized in thatblow molding method and apparatus for making a hollow plastic articleincludes forming a tubular element from a plastic material, severing andsealing a plastic core from the tubular element with the plastic corebeing disposed along a predetermined longitudinal axis, confining theplastic core in an open ended mold cavity while permitting the plasticcore to protrude out of the open ended mold cavity, deforming part ofthe protrusion back into the plastic core along the longitudinal axis toform a longitudinal bore in the plastic core, and shaping the remainingpart of the protrusion to form flat end walls on the plastic core.

An object of the present invention is to make a hollow plastic articleby permitting a portion of the plastic to expand outside a mold cavityand then deforming and shaping the protruding plastic.

This invention has another object in that a hollow FIG. 4 is a crosssection similar to FIG. 3 but showing the second step of operation;

FIG. 5 is a cross section similar to FIG. 4 but showing the third stepof operation;

plastic spool is manufactured by blowing portions of a BRIEF DESCRIPTIONOF THE DRAWINGS FIG. 1 is an exploded isometric view with parts brokenaway of blow molding apparatus embodying the present invention; I

FIG. 2 is an exploded horizontal cross section of a portion of FIG. 1showing the initial step of operation of the apparatus; I

FIG. 3 is a cross section taken along line3--3 of FIG.

FIG. 6 is a cross section similar to FIG. 5 but showing the fourth stepof operation;

FIG. 7 is a cross section taken along line 7-7 of FIG. 6; and

FIG. 8 is an isometric view with parts broken away and parts in sectionof the molded product removed from FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT For the sake of brevity,supporting frames for the mold sections, driving means, such ashydraulic cylinders, piping systems for circulating coolant in thethermoconductive mold sections, and other conventional mold componentsare not included in the following description since a variety of suchequipment may be utilized with the present invention. For a completeillus- 'number and may use only a single cavity. The opposite edges ofeach cavity define cutting edges 14 and 16; the opposite ends of thecavity 12 are enlarged by means of sloping portions 18 and 20 whichterminate in semicircular portions 22 and 24, respectively, (see FIG.2). Adjacent the cutting edges 14 and 16, the mold block 10 is slightlytapered so as to present sloping surfaces 26 and 28, respectively. Anaperture 30 is centrally located in each cavity 12 and extendscompletely through the mold block 10 as is shown in FIG. 2.

The mold block includes all the elements 12 through 28 described abovein connection with the mold block 10; however, such elements are notbeing separately described but merely identified with similar referencenumerals with 100 added. Thus, the corresponding elements for mold block100 are numbered from 112 through 128. The aperture 30 opening intocavity 12 does not have any corresponding aperture in the mating cavity112 as will become apparent hereinafter.

Above the sloping surface 26 (as viewed in FIG. 1), the mold block 10'has a projection 32 which in cross section is viewed as a truncatedangular configuration; a similar projection 34 is located below thesloping surface 28 and there is always such a projection on each side ofthe semi-cylindrical cavities 12 when a plurality 'of such cavities areutilized. A pair of recesses 133 and in the mold block 100 are shaped toconform to the projections 32 and 34, respectively, permitting the moldblocks 10 and 100 to be mated during a molding operation. I I

End plates 36 and 38 for each mold cavity are carried on core pins 40and 42, respectively, in such a manner as to permit unitary movement andrelative movement therebetween in accordance with a predeterminedsequence of operation. As is illustrated in FIG. 3, opposed faces of thecoring pins 40 and 42 are hollowed out in generally concaveconfigurations to define cutting edges 41 and 43, respectively. Thecoring pins 40 and 42 are movable axially by any suitable means, such ashydraulic actuators 44, one of which moves the coring pin 40 while anopposite one moves the coring pin 42, with both pins 40 and 42 beingreciprocated along a common axis defined by the longitudinal axis of themold cavity.

An extruder 50 having a die head 52 delivers an extrudate of plastic 54in tubular form along an axis transverse to the longitudinal axis ofeach mold cavity. Any moldable thermoplastic material may be utilizedfor the tubular plastic 54, such as polyethylene and the like. Thediameter of the tubular plastic 54 is controlled by pressurized airintroduced through the extruder 50 so that it will be larger than thelongitudinal axis of the mold cavity 12-112. Closure of the mold blocks10 and 100 causes the cutting edges 14-114 and 16-1 16 to cut thetubular plastic 54 and form a hollow plastic core 56 (see FIG. 2); theend plates 36 and 38 abut the mold blocks 10 and 100 to pinch offadjacent annular plastic flashes 57 from the core 56 while the core pincutting edges 41 and 43 sever a central portion 58 of the plastic core56. The product made by the blow molding apparatus is in the form of ahollow spool which is expanded in the mold cavity 12-112 by air from anair injection needle extending through the mold block aperture 30 andleaving a needle like opening 60 in the outer wall of the spool. As isshown in FIG. 8, the plastic spool has a hollow interior 62 with aninner cylindrical wall 64 defining a longitudinal bore extending betweenflat end walls 66 and 68; the outer wall of the spool is defined byannular flanges 70 and 72 extending from the end walls 66 and 68,respectively, and joining truncated conical walls 74 and 76,respectively, which are connected by an outer cylindrical wall 78.

The method of making the plastic spool shown in FIG. 8 will be describedin conjunction with the following description of the sequence ofoperation of the blow molding apparatus. The extrusion die 50 and diehead 52 delivers the tubular plastic 54 in between the opened moldblocks 10 and 100; as is shown in FIG. 1, the lower end of the tubularplastic is sealed into a flattened end by the block projections 32 andrecesses 133 from a previous molding cycle. As soon as the flattened endclears the lowermost portion of the mold blocks 10 and 100, a newmolding cycle commences and the mold blocks 10 and 100 are closed uponeach other. The cutting edges 14-114 and 16-116 on the mold blocks severa plastic core 56 from the tubular plastic 54, which core is confined inthe mold cavity 12-112 (FIG. 2). The initial position of the end plates36 and 38 and the core pins 40 and 42 are shown in FIG. 3 as beingslightly spaced from the protruding portion of the plastic core 56 ateach end thereof. Each core pin 40 and 42 is now moved by its respectivehydraulic actuator 44 in a direction toward each other against theprotrusions of the plastic core 56. Such core pins 40 and 42 moverelative to their respective end plates 36 and 38 so that eachprotrusion is deformed and folded back into the plastic core 56 alongthe longitudinal axis defined by the core pins 40 and 42 (FIG. 4). Therelative movement of the core pins and end plates during the initialforming step is limited by any suitablemeans, such as fixed collars (notshown) on the core pins 40 and 42. Thus, continued movement of the corepins 40 and 42 causes unitary movement of the respective end plates 36and 38 therewith during the completion of the inward stroke of each corepin.

During the unitary movement of each core pin and its end plate, thecutting edges 41 and 43 of the core pins move closer to each other toform the longitudinal bore 64 of the spool. FIG. 5 shows the end plates36 and 38 abutting the protrusion of the plastic core 56, afterwhich theend plates 36 and 38 continue to move until they abut the adjacent endsurfaces of the mold blocks 10 and 100. The completion of the inwardstroke of the end plates 36 and 38 and their core pins 40 and 42 isillustrated in FIG. 6, at which time an air injection needle (not shown)is inserted through the mold block aperture 30 and the plastic core 56forming the opening therein; air under pressure is now blown through theneedle into the spool interior 62 causing the plastic core to conform tothe shape of the mold cavity 12-112 and the end plates 26 and 38. Thecutting edges 41 and 43 meet at the completion of the inward stroke ofcore pins 40 and 42 and sever the excess plastic material 58therebetween resulting in the smooth bore 64 extending through theplastic spool.

In accordance with the foregoing method and apparatus, the plastic coreis confined by the mold cavity 12-112 in the X-Y plane as represented inFIG. 6 but is permitted to blow outside the mold cavity in the Z plane.The plastic which protrudes outside the mold cavity is engaged first bythe core pins 40 and 42 and then by the end plates 36 and 38 whichpermit final shaping of the spool end walls and which also pinch off theexcess flash material 57 that has blown completely outside mold cavity.This arrangement has the particular advantage that a finished spool ismade within the mold cavity and does not require any special operationor apparatus to remove flashing after the spool is released from themold.

Inasmuch as the present invention is subject to many variations,modifications and changes in detail, it is intended that all mattercontained in the foregoing description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is: i

1. Blow molding apparatus comprising:

a pair of opposed mating mold blocks cooperating with each other todefine a mold cavity opened at its opposite ends;

said mold blocks being movable against each other to house a hollowplastic core disposed in said mold cavity and having protrusionsextending out of said ends;

core pin means comprising a pair of core pins operatively disposed on acommon longitudinal axis and means moving said core pins into theopposite ends of said mold cavity into engagement with each other todeform part of the protrusions back into the plastic core and form alongitudinal bore therein; each core pin having a cutting edge whichengage each other to sever excess material from the plastic core in thelongitudinal bore; and an end plate carried by each of said core pinsfor closing the opposite ends of said mold cavity whereby the plasticcore may be finally shaped therein. 2. The apparatus as recited in claim1 wherein each core pin has an initial movement relative to its endplate and a final movement as a unit with its end plate operation onsaid plastic core.

4. The apparatus as recited in claim 3 wherein said end plates cooperatewith said mold blocks during final shaping of the plastic core to pinchoff excess flash material therefrom.

1. Blow molding apparatus comprising: a pair of opposed mating moldblocks cooperating with each other to define a mold cavity opened at itsopposite ends; said mold blocks being movable against each other tohouse a hollow plastic core disposed in said mold cavity and havingprotrusions extending out of said ends; core pin means comprising a pairof core pins operatively disposed on a common longitudinal axis andmeans moving said core pins into the opposite ends of said mold cavityinto engagement with each other to deform part of the protrusions backinto the plastic core and form a longitudinal bore therein; each corepin having a cutting edge which engage each other to sever excessmaterial from the plastic core in the longitudinal bore; and an endplate carried by each of said core pins for closing the opposite ends ofsaid mold cavity whereby the plastic core may be finally shaped therein.2. The apparatus as recited in claim 1 wherein each core pin has aninitial movement relative to its end plate and a final movement as aunit with its end plate to commence formation of the longitudinal borebefore commencing final shaping of the plastic core in the mold cavity.3. The apparatus as recited in claim 1 wherein said means moving saidcore pins effects such movement relative to said end plates during aninitial forming operation on said plastic core.
 4. The apparatus asrecited in claim 3 wherein said end plates cooperate with said moldblocks during final shaping of the plastic core to pinch off excessflash material therefrom.